In a commercially available assembly of this type the operating mechanism consists of two parallel, electrically driven ball screws which have their ball nuts connected to a toggle on the top side of the sliding surface. The toggle consists of a couple of links which can operate in two different relative positions, of which one, when the links are pulled together and stand at an angle to the sliding surface, can be used when, for example, a press tool is moved while it is resting on the sliding surface, while the second relative position, when the toggle is adjusted so that the links are in line with each other and with the sliding surface and thus can reach outside the sliding surface, is the one which has to be used for the tool to be transferred from the sliding surface to a press table or other support, just as when transferring in the opposite direction onto the sliding surface.
With each such transfer of large and heavy objects from or to a support the toggle has to be adjusted between these two working positions, and this adjustment requires that the ball screws operate while the object is lying still on the sliding surface. This discontinuous working manner delays and complicates the handling of the objects. Also, because of the design of the operating mechanism, the assembly is unnecessarily expensive.
It is also previously known to incorporate, in a forklift truck, a hydraulic-mechanical operating mechanism for handling press tools and the like. The forklift truck is made specially for the purpose and so cannot be used generally as a goods and transport vehicle. It therefore remains unused throughout the period which elapses in a plant between tool changes and similar operations that can be carried out with the truck. In addition to the fact that it is uneconomical, this forklift truck has the disadvantage that its operating mechanism operates hydraulically, i.e. it does not permit handling of heavy objects, such as are found in the engineering industry, of 1 meter or more.